"call apoc.load.html" with the same result
The apoc library has been partitioned into two versions, depending on the version you are using. Looks like this started in v4,1. Anyways, you must not have the full or extended version.
Looks like version 4.1 has a core and full version. You need the full version jar.
Looks like version 5 is broken into core and extended, where you need to add the extended to the core to get all the procedures/functions.
You can download the full and extended jars here.